Abstract

Fault-bounded amphibolite facies gneisses at Grey River, southern Newfoundland, yield a U/Pb zircon age of 686 +33/-15 Ma for the magmatic protolith, whereas metamorphic titanite from the same sample has an age of 579 ±10 Ma. Lower grade felsic tuffs north of the gneisses yield an age of 544 ±5 Ma and, unlike the gneisses, contain inherited Middle Proterozoic zircons. In the Roti Bay-Cinq Cerf Bay area, lithologically similar gneisses are intruded postmetamorphically by a granitoid complex, from which two plutons yield U-Pb zircon ages of 499 +3/-2 and 563 ±4 Ma.

These southern Hermitage flexure rocks are vestiges of a unique zone of late Precambrian-earliest Paleozoic crust, and they occupy a position intermediate between the lower Paleozoic Dunnage zone of the central mobile belt and the Precambrian Avalon zone. They may represent surface exposures of the seismically defined deep crustal block that underlies the eastern central mobile belt. These rocks can be correlated in age and tectonic position with rocks at the northwest margin of the Avalon zone elsewhere in the Canadian Appalachians and in Britain.